Wireless communication devices are becoming increasingly important for communication nowadays. Information and data can be transferred in a wireless communication network by using wireless communication devices. The wireless communication network includes one or more wireless communication devices and one or more base stations. A base station is a fixed device that is connected through a wired medium with other base stations. The base station provides wireless connectivity to wireless communication devices. Examples of wireless communication devices include, but are not limited to, a laptop computer, a personal wireless computer, a mobile phone, or a personal digital assistant (PDA). Determining the location of wireless communication devices has become a necessity for various purposes.
The location of a wireless communication device in the wireless communication network can be determined by using either a mobile-based or a server-based method. In the mobile-based method, calculations for determining the location are carried out at the wireless communication device. In the server-based method, calculation for determining the location-are carried out at a location-control server. Determination of the location of the wireless communication device in non-line of sight conditions may not be accurate. Non-line of sight conditions exist when the wireless communication device is not in the direct line of sight of a Global Positioning Satellite (GPS) or a base station. This can be overcome by utilizing the wireless communication network's infrastructure properties. For example, a ranging process can be used for power correction as well as time-synchronization of the wireless communication device with the wireless communication network.
A number of methods exist for determining the location of the wireless communication device. Most of these methods employ a triangulation method, which includes sending a message to three base stations simultaneously. The time taken by the message to reach the three base stations is measured and multiplied by the speed of light, which provides the distance between the wireless communication device and the three base stations. The distance between the wireless communication device and the three base stations is used to determine the location of the wireless communication device.
In one of the existing methods, the location of a wireless communication device in a Wireless Local Area Network (WLAN) is determined by using the triangulation method. This method does not, however, use the existing features of the WLAN to determine the location of the wireless communication device.
Another existing method for locating the wireless communication device in a wireless communication network uses the Time Difference of Arrival (TDOA) and the Frequency Difference of Arrival (FDOA). The distance between the wireless communication device and the three base stations is calculated by multiplying the TDOA with the speed of light. The TDOA is based on measuring the difference in a Time Of Arrival (TOA) of either of a three downlink signals received at the wireless communication device from the three base stations or can be based on the difference in the Time Of Arrival (TOA) of the uplink signals received at the three base stations from the wireless communication device. The difference in the TOA measurements of these signals is directly related to the distance differences between the wireless communication device and the three base stations. The distance differences thus calculated in the TDOA methods are used to compute the location of the wireless communication device. The FDOA is used for calculating the distance between the wireless communication device and the three base stations. The distance is calculated by dividing the speed of light by the FDOA. The FDOA is a frequency of the message received by the base station of the three base stations from the wireless communication device. The method is restricted to locating the wireless communication device, only when the wireless communication device is within the range of at least the three base stations.
In another existing method, the accuracy of locating a wireless communication device in a cellular communication system is determined. In this method, the location is determined by integrating information from an assisted GPS that is embedded in the wireless communication device and the properties of the cellular communication systems. The method is restricted to locating the wireless communication device, which is equipped with the assisted GPS. Further, the method is restricted since the assisted GPS embedded in the wireless communication device and the properties of the cellular communication system cannot be used independently of each other.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help, to improve an understanding of embodiments of the present invention.